Identification of Heritable Spermatozoal Degeneration within the Ductus Deferens of the Chicken (Gallus Domesticus)1

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Abstract
Low-fertility (LF) roosters were identified within a line of Delaware chickens. However, LF could be overcome by frequent insemination. Electron microscopy revealed numerous degenerate spermatozoa in LF Delaware semen. Therefore, LF was attributed to suboptimal numbers of functional spermatozoa within the oviduct. Spermatozoal degeneration was not induced (p greater than 0.05) when Leghorn spermatozoa were incubated with Delaware seminal plasma. Ejaculates from F1 roosters were screened for spermatozoal degeneration via uptake of ethidium bromide. Roosters were categorized as producing few, 4 +/- 1% (mean +/- SEM), or numerous, 43 +/- 6%, degenerate spermatozoa. Only roosters within the latter group were characterized by LF (p less than 0.001). When such F1 and F2 roosters were ejaculated daily for 5 days, the percentage of degenerate spermatozoa decreased to less than or equal to 5%. Low fertility was not observed (p greater than 0.05) with such semen from F2 roosters. When these roosters had resumed ejaculating numerous degenerate spermatozoa after a period of sexual rest, 3 representative roosters were killed. Each ductus deferens was subdivided into 9 sections, and spermatozoal integrity was determined for semen from each section. Degeneration commenced in the mid-ductus deferens and progressively increased towards the receptaculum. Thus, a genetic defect resulting in a shortened functional life of the spermatozoon within the ductus deferens has been identified.